Question

If a base-pair change occurs during DNA replication, this a. is a mutation. b. would be a mutation only if it falls in a protein-coding part of a gene. c. would be a mutation only if it falls in a transcribed part of the genome. d. is not a mutation, because only one base pair has been altered.

Short answer

The correct answer is a) a base-pair change that occurs during DNA replication is a mutation.

Step-by-step solution

Understanding DNA mutations

A mutation is a change in the DNA sequence that can lead to alterations in the final protein product. Mutations can occur during DNA replication when there is a mistake in the copying process, such as a change in a single base pair, insertion or deletion of a base, or rearrangement in the sequence.

Analyzing the given options

Option a: A base-pair change constitutes a mutation because it's a change in the DNA sequence. It may or may not have consequences on the final protein product depending on where this change has occurred. Option b: This statement is only partially correct, because a mutation can have consequences not only in protein-coding parts of a gene but also in regulatory elements that control the expression of genes. Option c: This statement is also partially correct, as not only transcribed parts of the genome can be affected by mutations, but also regulatory elements outside of the transcribed region that control the expression of genes. Option d: This statement is incorrect because a mutation can be a change in a single base pair. Whether it has any effect depends on where the change occurs in the DNA sequence. After analyzing all the options, we can identify the correct one.

Choosing the correct option

The correct answer is a) a base-pair change that occurs during DNA replication is a mutation.

Key concepts

DNA replication

DNA replication is a fundamental process that occurs within cells. It is through this process that DNA makes an exact copy of itself. This is crucial for cell division.
During replication, enzymes like DNA polymerase help in synthesizing new strands by matching each base on the template strand with a complimentary base. Thus, adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).

However, errors can sometimes occur during this copying process. These errors might involve mispairing of bases, leading to mutations. While the cell has many mechanisms to repair these errors, some might slip through, resulting in permanent changes to the DNA sequence. It is these changes or mutations that can potentially impact how a cell functions.

Mutation types

Mutations, which are changes in the DNA sequence, can arise in various forms. They can broadly be classified into a few categories:

• Substitution: A single base pair is replaced by another, such as an A-T base pair changing to G-C.
• Insertions: Additional base pairs are inserted into the DNA sequence.
• Deletions: Certain base pairs are removed from the DNA sequence.
• Frameshift: Insertions or deletions that are not in multiples of three can alter the reading frame of a gene, profoundly affecting the protein produced.

Some mutations may have little to no effect, while others can dramatically change the proteins produced by genes, possibly leading to diseases or beneficial traits. The effect of a mutation largely depends on its location and the function of the affected region.

Genomic sequence

The genome of an organism consists of all its DNA, encompassing all of its genes and non-coding regions. During DNA replication, any change in the genomic sequence constitutes a mutation.
Not all parts of the genome are protein-coding; there are vast areas that regulate gene expression or have unknown functions.
Changes in non-coding or regulatory parts can still influence cellular behavior by altering how genes are turned on or off.
Understanding which parts of the genomic sequence are affected by mutations helps in assessing potential effects on an organism's traits or health.

Protein-coding genes

Genes that contain the instructions to make proteins are called protein-coding genes. Proteins perform most of the cellular tasks and contribute to an organism’s structure and function.

Protein-coding genes go through transcription, where the DNA sequence is turned into messenger RNA (mRNA), and then translation, where mRNA is used to build proteins. Mutations in these genes can directly alter the type or function of proteins produced.

• Silent mutations might not change the protein at all.
• Missense mutations result in a different amino acid, potentially altering protein function.
• Nonsense mutations can create a premature stop codon, leading to incomplete proteins.

Whether within a protein-coding region or not, mutations still play a critical role in evolution, by introducing variation that could be subject to natural selection.